linux-kernel - Re: [PATCH] conditionally reschedule while loading selinux policy.

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Message-ID: <20130930172447.GA10562@redhat.com>
Date:	Mon, 30 Sep 2013 13:24:47 -0400
From:	Dave Jones <davej@...hat.com>
To:	Stephen Smalley <sds@...ho.nsa.gov>,
	Linux Kernel <linux-kernel@...r.kernel.org>, eparis@...hat.com,
	james.l.morris@...cle.com
Subject: Re: [PATCH] conditionally reschedule while loading selinux policy.

On Mon, Sep 16, 2013 at 02:40:30PM -0400, Dave Jones wrote:
 > On a slow machine (with debugging enabled), upgrading selinux policy may take
 > a considerable amount of time. Long enough that the softlockup detector
 > gets triggered.
 > 
 > The backtrace looks like this..
 > 
 >  > BUG: soft lockup - CPU#2 stuck for 23s! [load_policy:19045]
 >  > Call Trace:
 >  >  [<ffffffff81221ddf>] symcmp+0xf/0x20
 >  >  [<ffffffff81221c27>] hashtab_search+0x47/0x80
 >  >  [<ffffffff8122e96c>] mls_convert_context+0xdc/0x1c0
 >  >  [<ffffffff812294e8>] convert_context+0x378/0x460
 >  >  [<ffffffff81229170>] ? security_context_to_sid_core+0x240/0x240
 >  >  [<ffffffff812221b5>] sidtab_map+0x45/0x80
 >  >  [<ffffffff8122bb9f>] security_load_policy+0x3ff/0x580
 
With that patch applied, the problem seems to have moved elsewhere..

BUG: soft lockup - CPU#3 stuck for 22s! [load_policy:8119]
 irq event stamp: 1590886
 hardirqs last  enabled at (1590885): [<ffffffff8152c3dd>] __slab_alloc.constprop.78+0x4c0/0x4d7
 hardirqs last disabled at (1590886): [<ffffffff8153e06a>] apic_timer_interrupt+0x6a/0x80
 softirqs last  enabled at (1590336): [<ffffffff810480d9>] __do_softirq+0x169/0x200
 softirqs last disabled at (1590331): [<ffffffff8104839d>] irq_exit+0x11d/0x140
 RIP: 0010:[<ffffffff81223182>]  [<ffffffff81223182>] hashtab_insert+0x62/0x110

Call Trace:
 [<ffffffff812283b5>] policydb_read+0xc25/0x1200
 [<ffffffff810b1639>] ? is_module_text_address+0x19/0x40
 [<ffffffff8122cefe>] security_load_policy+0x10e/0x580
 [<ffffffff81078878>] ? sched_clock_cpu+0xa8/0x100
 [<ffffffff810786ad>] ? sched_clock_local+0x1d/0x80
 [<ffffffff81078878>] ? sched_clock_cpu+0xa8/0x100
 [<ffffffff810786ad>] ? sched_clock_local+0x1d/0x80
 [<ffffffff81078878>] ? sched_clock_cpu+0xa8/0x100
 [<ffffffff8103098a>] ? __change_page_attr_set_clr+0x82a/0xa50
 [<ffffffff81078878>] ? sched_clock_cpu+0xa8/0x100
 [<ffffffff8153669c>] ? retint_restore_args+0xe/0xe
 [<ffffffff810a196d>] ? trace_hardirqs_on_caller+0xfd/0x1c0
 [<ffffffff8127b07e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff810d2958>] ? rcu_irq_exit+0x68/0xb0
 [<ffffffff8153669c>] ? retint_restore_args+0xe/0xe
 [<ffffffff8121ff97>] sel_write_load+0xa7/0x770
 [<ffffffff811394c3>] ? vfs_write+0x1c3/0x200
 [<ffffffff812124de>] ? security_file_permission+0x1e/0xa0
 [<ffffffff811393bb>] vfs_write+0xbb/0x200
 [<ffffffff81158337>] ? fget_light+0x397/0x4b0
 [<ffffffff81139ab7>] SyS_write+0x47/0xa0
 [<ffffffff8153d634>] tracesys+0xdd/0xe2

We're holding a bunch of locks here, so we can't just cond_resched.  Thoughts ?

	Dave

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